Until Edward Snowden's files detailing the extent of state surveillance, the search engine received around 1.5m queries per day. But in the weeks and months following the Guardian's publication of the NSA files, the number of users more than doubled.

By November, more than 4 million people were using the site every day, and on Tuesday 7 January the site had its biggest day so far, serving 4,452,957 queries in a 24-hour period.